All our eggs in one basket
For a groundbreaking experiment with eggs, see weakly manipulated spacetimes. In addition to the fossil fuel problem, the real issue of course is that the human race still has all its eggs in this one little basket called planet Earth. This is more than just-a-bit-dodgy for all sorts of reasons. Here are just a few of them in no particular order: *The Supervolcano under the United States' Yellowstone National Park is thousands of years overdue for an eruption that could plunge the Earth into another ice age, from which a purely Earth-based human race may never recover so we really do need other self-sufficient colonies elsewhere that won't be affected, and which may be able to help speed Earth's recovery from the disaster if they have the energy and technology available to do so, which they of course will have. *Global warming or cooling, whether humankind is contributing to them or not, has the same potential outcome. If humankind is responsible for current climate change then we may be setting the Earth on a path to Runaway Global Warming ourselves, at which time human interference will not be able to stop the process. It is possible that runaway global warming would be able to increase global temperatures by several degrees which would melt the planet's remaining ice and raise sea levels so much that large swathes of the population would be killed or turned into refugees, leaving us with a population too small to consider colonizing space. It is even possible that runaway global warming could turn the Earth into an uninhabitable wasteland like our sister planet, Venus. Global cooling could of course send us into another ice age, which would stunt human evolution long enough for other disasters to have time to catch up with us. *As humans continue to pollute and otherwise change the biosphere, we are witnessing one of the fastest extinction events ever heard of. This is our entire food chain that is being affected by our activities, and it may easily reach a point where the food chain collapses. Couple this with increased desertification, drought, and running out of oil (which we use for pesticides, fertilizer and to power our farm machinery), all of which lead to increased farming difficulties, and it is clear that we need to reduce our polluting ways here on Earth, and move as much manufacturing off planet as possible. *There is also a danger that global overpopulation can make Humans lose their language and culture, see the anti-congestion argument. The fact that unintelligent behavior such as destroying the environment is a result of global overpopulation means that space colonization would make Humanity environmentally friendly, so there is no reason to fear cosmic ecocide. *With globalization of travel now virtually complete, if we get just one pandemic-level disease, it could spread across the entire planet in a matter of days, wiping out a great deal, or possibly all, of the world's population. There are a large number of other potentially extinction level events just lining up to exterminate the human race, and we cannot possibly tackle all of them head on. The level of technological and cultural development we have recently come to may be the only chance in the whole of human history (forwards or backwards) where we have the technical capability and energy availability to do the one thing that will help us to survive some of these problems: colonize local space and beyond.